Hearing devices are wearable hearing apparatuses which are used to assist the hard-of-hearing. In order to accommodate numerous individual requirements, various types of hearing devices are available such as behind-the-ear (BTE) hearing devices, hearing device with an external receiver (RIC: receiver in the canal) and in-the-ear (ITE) hearing devices, for example also concha hearing devices or completely-in-the-canal (ITE, CIC) hearing devices. The hearing devices listed as examples are worn on the outer ear or in the auditory canal. Bone conduction hearing aids, implantable or vibrotactile hearing aids are also available on the market. The damaged hearing is thus stimulated either mechanically or electrically.
The key components of hearing devices are principally an input converter, an amplifier and an output converter. The input converter is normally a receiving transducer e.g. a microphone and/or an electromagnetic receiver, e.g. an induction coil. The output converter is most frequently realized as an electroacoustic converter e.g. a miniature loudspeaker, or as an electromechanical converter e.g. a bone conduction hearing aid. The amplifier is usually integrated into a signal processing unit. This basic configuration is illustrated in FIG. 1 using the example of a behind-the-ear hearing device. One or a plurality of microphones 2 for recording ambient sound are built into a hearing device housing 1 to be worn behind the ear. A signal processing unit 3 which is also integrated into the hearing device housing 1 processes and amplifies the microphone signals. The output signal for the signal processing unit 3 is transmitted to a loudspeaker or receiver 4, which outputs an acoustic signal. Sound is transmitted through a sound tube, which is affixed in the auditory canal by means of an otoplastic, to the device wearer's eardrum. Power for the hearing device and in particular for the signal processing unit 3 is supplied by means of a battery 5 which is also integrated in the hearing device housing 1.
During the magnetic transmission of data (control data, programming data, audio data), E-field influences are unwanted since they may destructively overlay one another with the wanted signal from the magnetic field. The magnetic antennae (coil arrangements with and without ferrite core) as well as in particular their supply lines are affected by E-field injections. Conventional shields can generally not be deployed for use in miniaturized hearing devices for reasons of space and cost.
It is known to effectively shield E-fields with electrically conductive casings. The best known example of this is coaxial lines.
The patent application U.S. Pat. No. 6,940,466 B2 also discloses the shielding of ferrite cores with shielding films. This type of shielding of an antenna is associated with serious disadvantages particularly for hearing devices. The film surface namely has a high capacitive coupling to the windings arranged therebelow. The higher the working frequency, the lower the resistance of the alternating current resistor between the windings and the shielding film. This results in excessively high losses during emission and in a deterioration in the sensitivity during reception. If the capacitive coupling is to be kept to a minimum, the insulation must be selected to be very thick. As a result, the component becomes significantly larger and can no longer be used for miniaturized hearing devices.